docs: def percentile(self, n, default=None):
          """
          Calculate the Nth Percentile value over the time series.
  
          :param int n: Integer value of the percentile to calculate.
          :param default: Value to return as a default should the calculation not be possible.
          :return: Float representing the Nth percentile value or `None`.
          """
          return numpy.asscalar(numpy.percentile(self.values, n)) if self.values else default